This invention relates generally to the art of condenser and heat exchanger tube bundles, and more specifically to stakes for being inserted into lanes between rows of tubes within the condenser and heat exchanger tube bundles in order to dampen vibrations of, and provide support for, tubes in the rows.
It is well-known that tube bundles used in heat exchangers and condensers are prone to sympathetic vibrations and movement, as a consequence of high-velocity fluid, such as steam, flowing about the tubes as well as temperature and density changes within and outside of the tubes. Such vibrations are oscillatory in nature, and the oscillations can reach critical amplitudes and severely damage the tubes.
This problem is often encountered when a heat exchanger is refurbished by installing new tubes. For example, if a turbine heat exchanger, in which original tubes were of Admiralty brass or other relatively stiff materials, is refurbished (xe2x80x9cre-tubedxe2x80x9d) to have tubes of lighter weight noble metal materials, such as titanium, there is a good chance that undue vibrations will occur unless some remedial action is taken. Explaining this in more detail, heat-exchanger tube bundles have tube sheets at ends of the tubes and support plates at spaced intervals between the tube sheets. Both the tube sheets and the support plates have multiple holes drilled therein for receiving the tubes and holding them at the spaced intervals along their lengths. The tube sheets arc attached to and sealed with the tubes, but the intermediate support plates have larger holes so that there is some play about the tubes, which play allows the tubes to be inserted through the support plates during fabrication and refurbishing. A proper interval between the support plates is determined by a Design Guide published by the Heat Exchange Institute, which sets forth a maximum interval between support plates for tubes made of particular materials. When tubes of certain materials, such as titanium and stainless-steel for example, are placed in a heat exchanger that was originally designed with support-plate intervals for brass tubes, the interval spacings are often too great for the titanium or stainless-steel tubes, which, in turn, increases the potential for vibrations in the tubes.
Further, older heat exchangers often have changed dynamics as a result of re-tubing, which sometimes effectively changes the sizes of the holes in the support plates. This can also lead to increased vibrations.
An array of heat-exchanger tubes in a bundle normally has lanes between rows of tubes transverse to longitudinal axes of the tubes. These lanes are determined by patterns of holes in the tube sheets and the support plates.
One method which has been effectively used for damping vibrations of refurbished heat exchangers and condensers has been to insert stakes into these lanes approximately midway between the support plates for pressing against tubes on opposite sides of the lanes and thereby damping movements of spans of tubes between the support plates. This, of course, reduces vibrations. An example of such a stake is a Cradle Lock (registered trademark of The Atlantic Group, Inc.) stake which is disclosed in U.S. Pat. 4,919,199 to Robert B. Hahn. Bends of metal-strip stakes described in this patent turn them into leaf springs which provide resiliency to press against adjacent tubes, on opposite sides of the lane, and muffle their movement.
However, a bent metal strip stake of the type described in U.S. Pat. No. 4,919,199 will not work well where the width of a lane is too great or, similarly where its width expands outwardly to become too great. In such cases U-shaped stakes of the type disclosed in U.S. Pat. No. 5,213,155 to Robert B. Hahn have sometimes been used. These U-shaped stakes have two arms which extend along opposite sides of a row of tubes, with the arms being pulled together on the tubes by tie fasteners at points along the arms. Thus, each of the tubes in the row of tubes is dampened by the U-shaped stake""s interaction with tubes only in that row; which contrasts with the manner in which the stake of the U.S. Pat. No. 4,919,199 dampens tubes in a first row by interacting with tubes in a second row and vice versa. Such a U-shaped stake, although effective, is extremely time-consuming and expensive to install because it is difficult to apply the tie fasteners and because a U-shaped stake must normally be applied to each row of tubes as each tube is installed.
Stakes have also been structured to include first and second elongated bent metal strips held spaced from one another by rigid pins. Such stakes function substantially as do the individual bent metal strips of the stakes described in U.S. Pat. No. 4,919,199; that is they are inserted in lanes between adjacent rows of tubes with the bent metal strips, which form leaf springs as mentioned above, applying resilient pressure on the tubes of the adjacent rows. The rigid pins separating the bent metal strips increase the sizes of the stakes so that they can be used in wider lanes then can the stakes of U.S. Pat. No. 4,919,199. Also, the rigid pins of a single stake can be made of increasingly different lengths so that the bent metal strips extend on an angle to each other, thereby allowing the stake to be used in a lane having a tapered shape. Although such stakes have advantages in cases where the lanes are large and/or are tapered, and the tubes are evenly spaced, each individual stake is limited in use to lanes having widths within an unduly restricted width range.
It is, therefore, an object of this invention to provide a stake for use in heat exchangers and condensers which can be used in lanes within extremely large and varying width ranges. Similarly, it is an object of this invention to provide a stake having a broader application then do other known stakes, which therefore, in turn, reduces the number of stakes which must be made available for damping tube vibrations of condensers and heat exchangers.
According to principles of this invention, a stake for being inserted transversely into a lane between first and second rows of tubes in a tube bundle, for damping movement of the tubes in the bundle, includes first and second elongated metal strips, which are arranged with their inner sides facing one another, and a plurality of compression springs extending between the inner sides and being attached to the metal strips. With this structure, when the stake is inserted into a lane between first and second rows in the tube bundle, the first and second metal strips respectively contact tubes of the first and second rows, thereby compressing the springs which, in turn, urges, via the first and second elongated strips, the tubes of the first row away from the tubes of the second row, and vice versa. This, of course, dampens movement of the tubes in the first and second rows, thereby preventing vibrations. In one embodiment, the springs have progressively greater lengths so that the metal strips are tapered, one to the other. In the preferred embodiment the springs are coiled springs.
In one embodiment, each elongated metal strip has a V-shaped bend along its length so that the metal strips themselves are also resilient, and each of the elongated metal strips includes saddles on the outer sides thereof for engaging the tubes.